Circuit boards (often referred to as printed circuit boards) are used in various systems, such as computer systems, communication switch systems, and so forth. With modern technological advances, systems can be packed with electronic devices for different applications. In some cases, the different applications may involve use of signals in different frequency ranges.
A circuit board can have multiple signal layers having signal traces for routing signals associated with electronic devices mounted on the circuit board. Generally, wider signal traces are used to route signals of higher frequencies to avoid the skin loss effect in the signal trace. On the other hand, signal traces for routing signals having lower frequencies can have narrower widths.
It is desirable that the impedance of signal traces be generally the same even though they have different widths. The impedance of a signal trace is defined by the dimensions (thickness and width) of the signal trace, and the signal trace's distance from nearby reference plane(s). To achieve the same impedance, a wider signal trace has to be placed farther away from a reference plane.
As a result, to accommodate signal traces of varying widths for different applications, the overall thickness of a conventional circuit board will be increased, which will adversely impact circuit board fabrication cost and yield. Alternatively, some solutions have been directed at using a split circuit board design, in which an overall circuit board is split into multiple individual circuit boards that are connected together, with each individual circuit board optimized for the particular application. However, using multiple individual circuit boards is costly, and moreover, having to connect multiple individual circuit boards to form the overall circuit board adds to manufacturing complexity.